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From: Marton Balint <cus@passwd.hu>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when generating AES128 key
Date: Tue, 4 Jul 2023 21:30:29 +0200 (CEST)
Message-ID: <10991752-b1e9-41c0-623f-69ac11d994c9@passwd.hu> (raw)
In-Reply-To: <3b28f549-fc02-8ebf-de01-7dc1e0ae3c03@gmail.com>



On Tue, 4 Jul 2023, James Almer wrote:

> On 7/3/2023 6:52 PM, Marton Balint wrote:
>>
>>
>>  On Mon, 3 Jul 2023, Anton Khirnov wrote:
>>
>>>  Quoting Marton Balint (2023-07-03 22:54:41)
>>>>  On Mon, 3 Jul 2023, Anton Khirnov wrote:
>>>>  My patch use av_get_random_seed() which uses what the underlying OS
>>>>  provides, BCrypt for Windows, /dev/urandom for Linux, arc4random() for
>>>>  BSD/Mac.
>>>
>>>  IOW it's a jungle of various paths, some of which are not guaranteed to
>>>  be cryptographically secure. I see no such guarantees for arc4random()
>>
>>  It depends on OS and version most likely.
>>
>>>  from a brief web search, and the fallback get_generic_seed() certainly
>>>  is not either.
>>>  Granted it's only used on obscure architectures, but
>>>  still.
>>
>>  I am no expert on the subject, but even the generic code seems reasonably
>>  secure. It gathers entropy, it uses a crypto hash to get the output. And
>>  as you said, even that only used for obscure cases.
>> 
>>>
>>>  The doxy even says
>>>>  This function tries to provide a good seed at a best effort bases.
>>>
>>>>  You really think that these are significantly worse than
>>>>  OpenSSL/GCrypt, so it should not be allowed to fallback to?
>>>
>>>  I think we should be using cryptographically secure PRNG for generating
>>>  encryption keys, or fail when they are not available. If you want to get
>>>  rid of the openssl dependency, IMO the best solution is a new
>>>   int av_random(uint8_t* buf, size_t len);
>>>  that guarantees either cryptographically secure randomness or an error.
>>
>>  Sorry, seems a bit overdesign for me, so I won't be pursuing this further.
>
> I just sent a patchset implementing a new av_random() function that uses the 
> existing av_get_random_seed() entropy sources, and adds the ones used by 
> hlsenc too.
> If that goes in, then this patchset can go in as well afterwards.

Thanks! I will rework the patch to use av_random() then.

Regards,
Marton
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  reply	other threads:[~2023-07-04 19:33 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-02 19:30 Marton Balint
2023-07-02 19:30 ` [FFmpeg-devel] [PATCH 2/2] avformat/hlsenc: remove openssl/gcrypt random key generation Marton Balint
2023-07-03  2:21   ` Steven Liu
2023-07-03  2:20 ` [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when generating AES128 key Steven Liu
2023-07-03 19:23   ` Marton Balint
2023-07-03 19:33 ` James Almer
2023-07-03 20:15   ` Anton Khirnov
2023-07-03 20:54     ` Marton Balint
2023-07-03 21:09       ` Anton Khirnov
2023-07-03 21:52         ` Marton Balint
2023-07-04 19:02           ` James Almer
2023-07-04 19:30             ` Marton Balint [this message]
2023-07-06 17:01               ` [FFmpeg-devel] [PATCH] avformat/hlsenc: use av_random_bytes() for " Marton Balint
2023-07-14 19:39                 ` Marton Balint
2023-07-03 23:50         ` [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when " Michael Niedermayer
2023-07-04  5:54           ` Anton Khirnov
2023-07-04  9:08             ` Kieran Kunhya
2023-07-04 14:37             ` James Almer
2023-07-04 15:31               ` Anton Khirnov
2023-07-04 23:50             ` Michael Niedermayer
2023-07-05  9:22               ` Anton Khirnov
2023-07-05 22:54                 ` Michael Niedermayer
2023-07-06  7:52                   ` Anton Khirnov
2023-07-06 23:34                     ` Kieran Kunhya
2023-07-07  0:55                     ` Michael Niedermayer
2023-07-07  8:05                       ` Anton Khirnov
2023-07-07 14:42                         ` Michael Niedermayer
2023-07-03 20:20   ` Marton Balint

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